1. Field of the Invention
The present invention relates to an image transmitter, an image receiver and an image transmitting system that transmit or receive image data.
2. Related Art
In order to treat image data having high accuracy and high quality, it is necessary to transmit large volumes of image data. Since it is difficult to transmit large volumes of data by using single wiring, a plurality of wirings is actually used. When there are a number of wirings, the wiring area becomes larger, and a mounting cost of a printed wiring board increases.
In order to solve such a problem, a technology is discussed as the future problem (“AMLCD Manufacturing Technology” by S. S. Kim, pp. M-4/24 and M-4/26, in SID (Society for Information Display) Seminar (May 19, Baltimore, Md.) of the SID 2003, and “LCD television, The future Looks Bright for LCD TV, Information Display (Official Monthly Publication of SID)”, October 2003 Vol. 19, No. 10, FIG. 4 on page 13 by Joe Virginia). These discussed about the reduction of count of wirings to reduce the production cost.
Many interfaces are proposed as the data transmitting technology of countermeasure against EMI: for example, RSDS (Reduced Swing Differential Signaling), mini-LVDS (Low Voltage Differential Signaling), CMADS (Current Mode Advanced Differential Signaling), whisper BUS, Mobile-CMADS, MSDL (Mobile Shrink Data Link), MPL (Mobile Pixel Link), MVL (Mobile Video Interface).
These interfaces are proposed for reducing EMI. In these interfaces, its data size still cannot be efficiently reduced, because its image is transmitted in its original form of data without exploiting image correlation. The following papers are known in the society SID (Society for Information Displays): the paper about RSDS by Lee (see Integrated TFT-LCD Timing Controllers with RSDS Column Driver Interface, SID Digest 6.2, 1999), the paper about CMADA by Yusa (see High-Speed I/F for TFT-LCD Source Driver IC by CMADS, SID Digest. 9.4, 2001), and the paper by McCartney (see also the related art Japanese Patent Application Laid-Open No. 2003-44017). Further, the article is also published, which discussed the pros and cons about serial interfaces for cellular phones (see Whisper BUS: An Advanced Interconnect Link For TFT Column Driver Data, SID Digest. 9.3, 2001). Many interfaces such as Mobile-CMADS, MSDL, MPL and MVI are also developed for cellular phones.
Since image has less count of pixels at the present time, a count of wirings are successfully managed in reduction by devising something focusing only on circuits. However, this kind of devising is merely a short-term countermeasure by the following concern: as a count of pixels increases in future, the devising on circuit will be reached to its critical limit caused by the three (1) further rapid increase in a data size, (2) higher operation speed of circuits and (3) the additional circuit cost by both size and speed.
Power consumption is a key factor in electronic devices especially for cellular phones power-supplied by batteries. To reduce power consumption, higher operation of circuit is not desirable. Therefore, new unique technologies, but still hopefully inconsistent with the conventional one, shall be requested besides the conventional devising on circuits. The technology based on the principle of data compression is a one of candidate expected to be included in these new technologies. Then, the related arts will be reviewed.
A background art is disclosed in the Japanese Patent Application Laid-Open No. 2003-366107, which illustrates many options as data transmission method for LCD source driver including alternating bit inversion method to reduce data transition, Huffman coding, one-dimensional compression, and arithmetic coding to reduce data size. However, the technologies proposed above cannot always achieve the reduction ratio (that is, compression ratio) better than 1/2 because the attained data size is heavily dependent on data itself. Thus, this technology cannot be used for reducing the count of wirings.
Another background arts are disclosed in the two patents Japanese Patent Application Laid-Open No. 2002-202760 and 2001-166740, which apply a bus inverting technology: the technology reduces a data transition for EMI in transmission (the original data are bit-inverted to reduce transition count when transition count is over the half count of data lines). In these arts, the property of image data is not exploited so that its EMI suppression effect is very low, because that image data are treated as a general data when applying the bus inversion technology.
Another background art is disclosed in the Japanese patent Application Laid-Open No. 2000-152129, which illustrates a technology that executes the addition or subtraction to reduce a count of data transition. In the art, the addition of “1” to data value will reduce a count of transition. For example, consider the case that a data transition from 0000 to 1111 is converted to the data transition from 0001 to 0000. The count is reduced 4 to 1. In the art, the property of image data is not exploited so that its EMI suppression effect is very low, because that data are treated as a general data (not as image data) when applying the addition or subtraction.
Another background art is proposed by the paper by Jun Yang, Rajiv Gupta, “FV Encoding for low-power Data I/O, IEEE, ISLPED 2001”, which illustrates a FV coding method that carries out bus inversion by monitoring occurrence frequency of data in a dynamic manner. This method does not also exploit the statistical property of images.
Another background art is disclosed in the Japanese patent Application Laid-Open No. 2003-44017, which illustrates a non-transmission method to reduce the size of data to be transmitted: there is no need to transmit data when data has the same value as that of data found on one horizontal line (1H) before (this data is called as “1H-previous”) and the stored 1H-previous data are reused in the receiver (i.e., the source driver). There is averagely about 10% to 20% in actual images for the possibility that data has the same value as 1H-previous. This suggests that the data size can be reduced by 20% at most by this non-transmission. As a result, this method is not powerful enough for the reduction of count of wirings.
Another background arts are disclosed in the Japanese Patent Application Laid-Open No. 2000-20031 and 2003-131627, that illustrate a methods of reducing EMI by using the IH correlation of image. See also the SID IDRC 2003 paper “Vertically Differential EMI Compression Method for High Resolution LCDs” by the same authors Haruhiko Okumura et al. With these methods, a data size and a count of wirings cannot be reduced enough too.
Even when the best is selected in the above conventional technologies that generally believed to achieve an effective compression or EMI suppression with keeping additional hardware modifications small, a count of wirings cannot be efficiently reduced. Then, further investigation will be given on advanced approaches with admitting slightly larger hardware as follows.
The most advanced data compression technology without data loss (lossless) is FCD14495 (ISO standard). It is also known as JPEG-LS (JPEG-lossless). Even with this technology, averagely the compression of 1/2 is achieved to the utmost. It seems apparent at a first glance that a count of wirings could be reduced easily to half. But since a data compression rate greatly fluctuates due to image data itself, in fact, it is quite difficult to reduce a count of wirings to half. As data loss is not allowed, when trying to reduce a count of wirings even the reduction to 1/2 is impossible by considering a worst case of fluctuation on images. Therefore, this technology is not a desirable selection under preset circumstances.
In connection with a data compressing technology, a DPCM (Differential Pulse Coded Modulation) technology is proposed. As a predictor on DPCM technology relating to image data, MED (Median edge detector) and GAP (gradient-adjusted predictor) are widely known. Since the GAP requires a 2H memory and the size of hardware is large, MED will be exploited here thanks to its 1H memory. Then, conventional technologies relating to MED will be investigated as follows.
MED is the technology adopted by JPEG-LS, and it is still under the further development in the recent years. A new modification improves the performance of MED by using diagonal edges in images (see the paper by Jiang et al. “Revisiting the JPEG-LS prediction scheme, IEEE Proc. Visual Image Signal Process, Vol. 147, No. 6, December 2000, pp. 575-580). Further, other modifications of MED improve the performance according to new prediction schemes (see the paper by Grecos et al. “Two Low Cost Algorithms for Improved Diagonal Edge Detection in JPEG-LS, IEEE Transaction on Consumer Electronics, Vol. 47, No. 3, August 2001, pp. 466-473 and Toward improved prediction accuracy in JPEG-LS, SPIE Optical Engineering by Jiang et al., 41(2) 335-341 (February 2002)). Another high-performance MED is also introduced (see the paper by Edirisinghe “Improvements to JPEG-LS via diagonal edge based prediction, Visual Communications and Image Processing 2002, Proceedings of SPIE Vol. 4671 (2002)).
The conventional MED and its variations mentioned above have been used only for the purpose of data compression. On the other hands, they are not used for the purpose of transmitting image data in aiming to low power consumption: that is, the present invention shall exploit MED for the transmission with aiming to low power.
A similar technology is proposed recently in the paper (We-Chung Cheng and Massound Pedram, Chromatic Encoding: a Low Power Encoding Techniques for Digital Visual Interface IEEE DATE 2003, session 6.3), which illustrates a chromatic encoding technology that reduces power consumption using the entropy of an image for DVI (Digital Visual Interface). As this technology premises the transmission interface DVI, it is the modification of TMDS coding so that it is also based on the three premises of DVI: (1) binary data transmission, (2) long length of wiring to transmit data and (3) realization of high-speed operation of data transmitting circuit.
Now following review will be given on the arts to clarify another aspect of the present invention. In general, a multi-valued transmission technology (which transmits data with multi-value) is expected as the image data transmitting technology. In an image data transmitter such as transmission for LCD source driver, there is no transmitting technology that aggressively exploits both multi-valuation and the properties of image correlation. The related arts of multi-valuation will be given as follows.
A background art is disclosed in the U.S. Pat. Publication No. 6,339,622, which illustrates a data transmitting system that realizes multi-valued data transmission in an LCD driver. This system adopts a technology, which converts data into ternary values (3-valued values). However, in this system, a count of wirings is not changed because that the effect for reducing a count of wirings is not obtained by the ternary valuation: ternary values are processed by two bits. In this system, since the properties of images are not aggressively exploited, its performance is poor
Meanwhile, a multi-valued logic circuit in an electric current mode is proposed (see Current-Mode CMOS Multiple-Valued Logic Circuits by Wayne Current, IEEE Journal of Solid-State Circuits, Vol. 29, No. 2, February 1994, pp. 95-107). Further, other technologies about multi-valued transmission are proposed (see R. Fajad-Rad, C-K. Ken Yang, M. A. Horowiz and T. H. Lee, A0.3-μm CMOS 8-Gb/s 4-PAM Serial Link Transceiver, IEEE Journal of Solid-State Circuits, Vol. 33, No. 5, May 2000, and S. Srinivasan, Circuit & Signaling Strategies for on-chip interconnects in DSM CMOS, submitted to the Graduate school of the University of Massachusetts Amherst in partial fulfillment of the requirements of the degree of master of science in electrical and computer engineering, August 2002). In these documents, the multi-valuation mainly means 3 (ternary) values and 4 (quaternary) values, and 16 or higher values are hardly used. This comes from the fact that higher level of multi-valuation is not desirable for actual application: as a level of multi-valuation becomes higher and higher, the power consumption increases. This is a serious problem for multi-valued transmission.
The all above technologies are different from the present invention by the inventors, because the present invention is based on both multi-valued transmission and exploitation of the image correlation.